Disruptions which have occurred in recent years in the supply of petrochemical fuels have brought about an extensive search for alternate fuel sources. Considerable attention has been focused on the use of alcohol produced by biomass fermentation (e.g., fermentation of agricultural wastes) as a substitute fuel. Alcohols make excellent fuels. The constant renewal of biomass sources which can be fermented to produce alcohol could produce massive supplies of fuel in perpetuity. However, biomass fermentation to produce alcohol yields only solutions containing relatively low concentrations of alcohol, usually between about 10 and about 15%. Before the alcohol can be used as a fuel, it must be separated from the remainder of the fermentation liquor.
Separation of such liquid mixtures is an age-old technical problem. Distillation is a well known way of separating and purifying liquids. Traditional distillation methods are, however, relatively inefficient from an energy standpoint. When traditional distillation technologies are utilized to separate the alcohol from a fermentation liquor, disproportionate amounts of energy are consumed. Some workers have reported that when the energy required for cultivation and transportation of the necessary biomass is included with the energy consumed in distilling the alcohol from the fermentation liquor, the total amount of energy consumed may be greater than the energy content of the alcohol produced.
Numerous efforts have been made to develop more efficient distillation processes. Attempts have been made to increase efficiencies by returning part of the heat of condensation of distilled vapors back to the distilland liquid to promote further evaporation (see Harding, et al., U.S. Pat. No. 3,032,481). Distillation systems have also been developed for producing fresh water from seawater which attempt to conserve energy by recovering a portion of the heat of condensation of the distilled liquid (see Mahistre, U.S. Pat. No. 3,494,835). Other workers have attempted to use solar energy to distill liquids such as seawater (see Duffy, U.S. Pat. No. 3,330,740).
Such systems have not proved completely satisfactory. In may cases, large, complex and prohibitively expensive apparatus has been required. In other cases, thermal efficiencies are still too low for effective operation. There remains a real need for a simple, relatively small, functional and highly economical distillation system which can be used to separate alcohol from aqueous fermentation liquors.